Ground heat exchanger

ABSTRACT

The invention relates to a ground heat exchanger utilizing the geothermal energy of the ground, comprising pipe conduits and channels mounted within a support structure. According to the invention, a layer of air-permeable materials is formed on the virgin soil ( 1 ), horizontally and/or at a small inclination angle relative to the horizontal direction, creating a circulation channel ( 9 ) of the exchanger, the channel being confined by a support slab ( 14 ) with spacer elements ( 11 ) coupled with a construction net ( 8 ) seated onto a stabilizing net ( 7 ), the whole structure being covered by an insulating layer ( 19 ). Furthermore, the heat exchanger is equipped with a collector of the process air having an appropriate shape.

The invention relates to a ground heat exchanger utilizing thegeothermal energy of the ground in which the heat exchanger is seated ata certain depth. The heat exchanger may constitute an element of aventilation system of an apartment or office/factory building, in whicha collector directs the process air to the ventilation system of thebuilding.

From Polish patent application No. 119749 one knows a cooling/heatingdevice employing the heat energy of the ground for cooling or heatingthe air. The device comprises vertical air intakes made in the ground,preferably in the form of wells. Lower ends of the wells are connectedto a collecting chamber via conduits seated in a layer of the ground, orvia a layer of the ground having small flow resistance and good thermalconductivity. The collector of the exchanger is composed from conduitswith circular cross-section, laid in a layer of the ground and alsoconnected to the collecting chamber. The collecting chamber is connectedto a technological device, such as an air-cooled liquefier, cooler ofwater, an air-conditioning or ventilation device.

The cited invention allows for significant energy savings, particularlyduring periods of maximum or minimum temperature of the atmospheric air.

Another embodiment of a system for heating and ventilation of a buildingis known from PCT/SE95/00569. According to that invention, a buildinghas a peripheral foundation wall or has peripheral foundation beams, onwhich external wall and the floor of the building rest, the floordefining the residential floor areas in the building. A room is situatedbelow the floor within the contour of the foundations. Openings orapertures—circulation conduits are made in the floor, through which airof desired parameters is circulated from the room below the floor todwellings of the building. An air chamber is located below the floorslab, the air chamber being connected to the conduit directing the air.The chamber is closed with a membrane in a form of a tight barrier madefrom a plastic material. The membrane is seated on a porous layer, whichis air-permeable, the layer having a form of a gravel prime coat andbeing situated at least on the portion of the support area of the groundbelow the foundation wall.

The invention relates to a ground heat exchanger, in which a stabilizinglayer of a material with good thermal conductivity is formed in thevirgin soil, the layer being located horizontally or at a small anglerelative to the horizontal direction. The layer of the material has aform of a gravel prime coat and/or a square stone prime coat, which isfilled with sand to increase the contact area with the air. The layercreates a circulation channel of the exchanger with the support slab.The slab has spacer elements, which are coupled with the constructionnet seated onto the stabilizing net, which covers the layer of theair-permeable material. The air intake and the exhaust channel haveencased temperature, humidity, flow rate sensors and other necessarymeasuring devices. The whole structure, except to the contour of theintake and the exhaust channel, is covered with an insulating layer,preferably made from foamed polystyrene.

The collector of the heat exchanger according to the invention,directing the process air, comprises generally a plane of the flow ofthe process air and an air-distributing element. The cross-section ofthe element has a form of a sector confined by any curve, preferably itis a circular sector or any other geometric figure. The element isconfined by a support point on the side of the process air inlet, whileits opposite point is a bear point. The element is made from a metal oranother material, preferably from polypropylene and/or a thermoplasticmaterial. The longitudinal section of the element has any shape, howeverits modular length depends on acceptable technological parameters of thefollowing air. The foundation slab with openwork apertures and/or thestabilizing net seated onto the gravel prime coat defines the airflowplane.

In so encased space, the spatial position of the element, with mutualposition of the points relative to the airflow plane, is of fundamentalimportance for obtained technological and strength properties.

According to the invention, the support point is situated above theairflow plane or in the airflow plane, while the bear point is seatedabove the airflow plane, and another bear point is seated in the saidairflow plane, and also, as the third possibility, the bear point ispositioned below the airflow plane.

The optimal position of the element is if the support point ispositioned in the airflow plane. An appropriate number of open and/orclosed channels, having appropriate shapes, are made in the side wall ofthe element on the side of the air inflow. The inner surface of theelement is lined with a coat of an antistatic and/or antibacterialmaterial. The technological parameters are controlled by temperature,pressure, humidity and flow rate sensors. An air moistener is locatedwithin the inventive element, axially and longitudinally, and a UV lightsource and iodine micronutrients dispensers are located along the airmoistener.

Preferably, the element has a shape of circular sector, and the supportpoint is positioned above the airflow plane, while the bear point ispositioned in this plane, the footing of the element being seated in atray in a form of a channel guide with strut-seal elements. The guide isseated indirectly on a spacer bracket, preferably in a form of a T-barand/or on another bearing structure.

According to the invention, the air introduced into dwellings flowsperipherally around the floor, this creating the appropriate aircirculation. By directing the exhaust through the foundations of thebuilding and heating up its lower portions, one can avoid detrimentalmoistening of the building and the foundations.

The structure of the ground heat exchanger according the inventionguarantees the contact of the whole volume of the circulating airdirectly with the ground. As a result of employing the heat exchangerequipped with a collector according to the invention, one obtainssignificant savings of heating, investment and operation costs,preserving a preferable microclimate of the ventilated building.

A very good and recommended supplemental for the ventilation system forprivate house building is mounting a ground heat exchanger outside theventilated building. The heat exchanger employs the phenomena of theconstancy of the year-round ground temperature (at a level of about 10°C.) at a depth of 6 to 10 m below the ground surface.

The invention will be better appreciated by reading the followingdescription of preferred embodiment in conjunction with accompanyingdrawings of which:

FIG. 1 shows a segment of a ground heat exchanger according to theinvention in a cross-sectional view.

FIG. 2 shows a joint of a collector with a slab of a ground heatexchanger in a cross-sectional view.

FIG. 3 shows a cross-sectional view of an air-distributing element.

FIG. 4 shows a cross-sectional view of a collector in the case of theelement having a form of a circular sector and the airflow plane beingthe foundation slab.

FIG. 5 shows an air-distributing element in an axonometric projection.

FIG. 6 shows a mounting of the element footing in a guide.

FIG. 7 shows a cross-sectional view of the encased element

FIG. 8 shows a cross-sectional view of the encased element mounted inthe airflow plane.

According to the invention, a ground heat exchanger is located in anexcavation at an optimal, technological depth, necessarily above theground water level. As it results from FIG. 1, properly compacted virginsoil 1 defines a surface 2 of a prime coat creating a foundation of aheat exchanger. The surface 2 is positioned horizontally or is slightlyinclined relative to the horizontal direction in the appropriatedirection. The direction of the inclination of the surface 2 relative tothe surface of the virgin soil 1 depends on the mutual position and thewhole` configuration of the exchanger.

A gravel prime coat 4, poured loosely without compaction, is laid ontothe surface 2. Dimensions of the gravel grains in the prime coat 4increase from the surface 2 and range from 5 to 20 mm. Square stoneprime coat 5 or grit prime coat may be employed instead of the gravelprime coat 4. Thickness of the gravel prime coat 4 as well as the squarestone prime coat 5 is about 20 to 60 cm, this resulting from calculationof the efficiency of the heat exchanger according the invention. Freespaces in the gravel prime coat 4 as well as in the square stone primecoat 5 should be filled with rinsed sand 6. The sand 6 fills free spacesbetween the gravel grains or stones increasing the thermal conductivityof the prime coat. So formed prime coat layer exhibits good thermalconductivity and a small airflow resistance.

A stabilizing net 7 made from a thermoplastic material is laid on soformed layer of the aggregate. The shapes and dimensions of the meshesof the net 7 depend on the employed aggregate, preferably the dimensionsshould be smaller than dimensions of the grains of the aggregate the netrests on, the mesh dimension being 10 mm, for example. A constructionnet 8 with ca. 20-70mm meshes is freely laid on the net 7, to transferthe load of the remaining structure of the heat exchanger and soillayers 18 onto the virgin soil 1.

The basic element of the heat exchanger is a circulation channel 9, theheight of which is constant and dimensioned by the module size—theefficiency of the exchanger. The channel 9 is confined by the net 8 viaa spacer element 11. The spacer element 11 is joined to the net 8, forexample by welding of plastic elements. The support slab 14 has theappropriate length, and for preserving the modularity of the heatexchanger the support slabs 14 may mutually overlap 14.1. For example,the channel 9 has a height from 20 to 40 mm for given size of the moduleand technological parameters of the exchanger, for example for the airflow rate of 1.0-3.0 ms

The support slab 14 is a basic and a repeatable module of the exchanger.Exemplary size of the slab 14 is 1.9×1.9 m and for the air flow rate ofthe order of 400 m³/h nine such slabs 14 should be mounted in theexchanger. The cross-sections of the spacer elements 11 have shape ofany geometrical figure. Most preferably, the shape is a trapezoid, thelower base of which, i.e. the shorter side 12, is joined inseparably tothe net 8, creating a supporting, stiff, spatial structure with the slab14. The number of the elements 11 and the positions of on the slab 14 aswell as their dimensions depend on the load transferred by theexchanger. Channel trays 15 are mounted at the ends of the slab 14 andon the net 7, in which the endings of the air-distributing elements 13are located, while a pipe 16 delivering the air to the channel 9 isplaced within the element 13.

An appropriate soil layer 18 is laid onto so formed exchanger, and,still above, a technological insulating layer 19 to uplift the isothermsof 8-12° C. Most preferably, the layer 19 is made from foamedpolystyrene, and a film 20 made from a plastic material is placed on thelayer 19. The layer 19 and the film 20 play a role of an insulatoreliminating the temperature difference.

The air intake 21 is formed above the ground level and equipped with afilter 23, most preferably a non-woven filter, for removing dust andallergens. The air intake 21 and the exhaust channel 22 are equippedwith temperature sensors 24, flow rate sensors 25 and humidity sensors26.

The external air is taken, for example, by a metal air intake 21equipped with a nonwoven air filter, at least of a class EU3. Next, theair is flowing into the element 13, having a semicircle shape in thisembodiment, being the ceiling for the flowing air. From below, the airhas a direct contact with the layer of the gravel prime coat 4 or squarestone prime coat 5 covered with sand 6. In the channel 9 the essentialexchange of heat and humidity between the flowing air and the graveland/or stones 5 covered with sand 6 occurs. Then, the air is collectedto the collecting channel 17 and further to the ventilation system ofthe building. The flow rate of the air flowing through the air exchangersegment is of the order of 1.0-3.0 m/s. The number of segments for anindividual air exchanger is selected basing on the planned efficiency ofthe exchanger. The amount of the flowing air should be divided by 20-40m³ per one segment for 24 hours per day of operation of the exchanger.For example, for the flow rate of 400 m³/h nine segments should beemployed.

Research and tests confirmed the extraordinary efficiency of theinventive heat exchanger. For example, for an exchanger seated at adepth of 6-7 m, the air is heated by 2-6° C. and is humidified by thehumidity coming from the ground to 80-92% at an ambient temperature of−20° C. The humidity of the air, after heating up in the building toabout 20° C., is in the range of 30-35%. On the other hand, during thesummer heatwaves, the air is cooled down, for example from 34° C. to atemperature of 15-17° C. and the air humidity is increased from 55% to98-100%. The humidity of the air introduced to a building is of theorder of 55% for 26° C. The condensate produced during the coolingprocess enters directly the ground or is drained from the surface 2 ofthe prime coat and the layer 19 via drainage pipes 3. As research andtests showed, the maximum amount of the condensate is 0.8 l/m² of thesegment area, this giving an amount of 6 to 10 liters per 24 hours ofoperation.

The collector of the process air, as shown in FIG. 2, comprisesgenerally two portions, mutually dependent and coupled technologically,these being a foundation slab 10 and an upper, exchangeable encasingelement in a form of the air-distributing element 13.

The element 13, due to the employed construction material, i.e., a metalas well as due to the size of the collector, takes various shapes, shownin a cross-sectional view in FIG. 3. Preferably, the element 13 is madefrom a plastic material, particularly polypropylene and/or athermoplastic material. So, its cross-section is a sector of any curve13.1 or any figure 13.2 and is confined from the side of the air inlet Dby a support point A and an opposite bear point B. Exemplary curves 13.1are circular sector 13.1.1 or ellipse sector 13.1.2, and geometricalfigure sectors are rectangular sector 13.2.2 or triangle sector 13.2.2.The plane of the flow of the process air D is denoted by the letter C.The plane C is created indirectly by the stabilizing net 7 mounted onthe construction net 8. In the case of different technologies of the airprocessing, the same plane C is created y the foundation slab 10, as aferroconcrete or concrete slab with openwork openings 10.1. Thestructure of the slab C depends on the operation mode of the collectorand technological demands imposed on the parameters of the process airD. In exemplary, optimal embodiment, if the element 13 has cross-sectionshaped as a circular sector 13.1, the mutual position of the points Aand B may be diversified, as shown in FIG. 7. As is apparent from thefigure, the point A may be situated above the plane C, the point A1 maybe situated in the plane C, the point B1 is situated above the plane C,the point B2 in the plane C, while the point B3 may be situated on anappropriate structure mounted below the plane C. FIG 6 shows anembodiment of the invention, in which the point A1 is situated in theplane C, this requiring to have closed channels 27 and/or open channelsfor desired amount of the air D made in the element 13 on the side ofthe air D inlet. FIG. 5 shows the encasement of the inner surface 29 ofthe element 13, which is lined with an antistatic agent 30 and/orantibacterial agent 31.

The technological demands imposed by standards for the process air Drequire to have a proper number and a proper configuration oftechnological temperature sensors 24, as well as pressure, humidity andflow rate sensors mounted in the element 13. Also, FIG. 8 shows amoistener 32 placed within the element 13, axially and longitudinally inthe plane C, and a UV light source 33 and an iodine micronutrientsdispenser are located along the air moistener 34.

The load of the soil layer 18 is transferred by the element 13, andtherefore one of a plurality of possible solutions of mounting twofootings 35 of the element 13 in a channel tray 15 has been elaborated.The channel tray 15, as shown in FIG. 4, comprises strut-seal elements15.1 which allow for controlled movement of the footing 35 under theloads, preserving watertightness and stable stiffness of the element 13.Depending on the position of the points A and B, the tray 15 may bemounted indirectly on a spacer bracket 36, e.g. a ferroconcrete footingfor points B.

As already mentioned above, FIG. 2 shows a cross-section of a sector ofthe ground heat exchanger, from which the process air is flowing out, toa user via the collector for the process air according to the invention.A layer of a height 3-10 cm is properly laid on the virgin soil 1 and agravel prime coat 4 of a height 3-10 cm, on which rest the constructionnet 8 and the stabilizing net 7, which defines the plane C. The supportslab 14 is supported by the bracket—spacer element 11, the space, asalready explained in reference to FIG. 1, defining the circulationchannel 9 for the process air D, of a height in the range 2-5 cm. Theslab 14, preferably made from polypropylene, transfers the load of thechannel tray 15, playing a role of a guide via the space bracket 36, tothe virgin soil 1. Preferably, the spacer bracket 36 has T-barcross-section; however, due to strength considerations it may takedifferent shapes, such as close sections, for example. Here, in thedescribed structure of the collector, the element 13 has a shape of acircular sector 13.1. with a diameter of 30-80 cm, and its modularlength is preferably 100 cm. A layer of soil 18 of a thickness more than15 cm is located above the element 13, “encased” below the insulatinglayer 19 made from foamed polystyrene as the insulation for the groundisotherm.

The application of the ground heat exchanger according to the inventionin the Polish climatic zone and similar zones gives benefits both in thesummer and the winter. It allows for the utilization of the coolness ofthe ground to lower the air temperature during summer heatwaves totemperatures allowing for effective dehumidification of the airdelivered to the building.

During the season of heating, the fresh air is initially heated in theheat exchanger and is humidified by direct contact with the ground. Theplastic material used to build the heat exchanger makes the stream ofthe air to be properly formed. The material for slabs and the nets is athermoplastic material with an addition of an antibacterial agent basedon silver and/or gold oxides. Besides lowering the heating costs, theheat exchanger according to the invention improves the microclimateinside the ventilated building, because it prevents from excessivedrying of the air in the winter.

1. A ground heat exchanger utilizing the thermal energy of the ground,comprising pipe conduits and channels mounted within a supportstructure, characterized in that a layer of air-permeable materials isformed on the virgin soil, horizontally and/or at a small inclinationangle relative to the horizontal direction, creating a circulationchannel of the exchanger, the channel being confined by a support slabwith spacer elements coupled with a construction net seated onto astabilizing net, the whole structure being covered by an insulatinglayer.
 2. A heat exchanger according to claim 1, characterized in thatthe layer of air-permeable materials has a form of a gravel prime coatand/or a square stone prime coat and is filled with sand, and its lengthjust bigger than the length of the support slab or its portion.
 3. Aheat exchanger according to claim 1, characterized in that a temperaturesensor, a humidity sensor, and a flow rate sensor are all encased at anair intake and an exhaust channel.
 4. A heat exchanger according toclaim 1, characterized in that it comprises a collector of process air,coupled with the circulation channel, which consists of a plane of theflow of the process air and an air-distributing element, thecross-section of the element having a shape of any curve or anygeometric figure, and the element being confined by a support point on aside of the process air inlet and by an opposite bear point, the elementbeing made from a metal or non-metallic material, having arbitrary shapeof the longitudinal cross-section, and its length being conditioned bytechnological parameter of the air flowing therethrough.
 5. The heatexchanger according to claim 4, in that the cross-section of the elementis a circular sector, and the support point is situated above the plane,a first in-plane point is situated in the plane, and an upper point issituated above the plane, a second in-plane point is situated in theplane, and a lower point is situated below the plane, and, moreover,channels having an appropriate shape are made in the element on a sideof the air intake.
 6. The heat exchanger according to claim 4,characterized in that the plane is defined by a foundation slab having aform of a ferroconcrete and/or concrete slab with openwork openingsand/or with a stabilizing net and with a gravel prime coat, and theelement is made, from polypropylene and/or thermoplastic material. 7.The heat exchanger according to claim 4, characterized in that an innersurface of the element is lined with a coat of an antistatic agentand/or a coat of an antibacterial agent, and sensors of temperature,pressure, and flow rate of the air are mounted in the element, and anair moistener is mounted within the element, axially and longitudinally,in the plane and a UV light source iodine micronutrients dispensers arelocated along the air moistener.
 8. The heat exchanger according toclaim 4, characterized in that the element has a shape of a circularsection, positioned according to the support points and the secondin-plane point, footings of which are seated in a channel tray withstrut-seal elements the channel tray being seated indirectly on a spacerbracket in a form of a T-bar and/or another bearing structure, and atthe support point the element has channels.
 9. The heat exchangeraccording to claim 5, characterized in that the element has a shape of acircular section, positioned according to the support point and thesecond in-plane point, footings of which are seated in a channel traywith strut-seal elements, the channel tray being seated indirectly on aspacer bracket, in a form of a T-bar and/or another bearing structure,and at the support point the element has channels.
 10. The heatexchanger according to claim 5, in which the channels are closedchannels.
 11. The heat exchanger according to claim 5, in which thechannels are open channels.